How Depression Affects the Brain

Every year well over 200 million prescriptions are handed out for antidepressants in the United States. Of the people who take antidepressant medications some will feel a certain level of relief and some won't benefit at all. So, if depression is simply due to an imbalance in neurotransmitters, why are some people ‘treatment resistant' when they take the very medication designed to correct the problem?

Professor Eva Redi, of the Northwestern University Feinberg School of Medicine, believes the answer lies in the faulty assumptions people have been making about the nature of both stress and depression. During the 2009 Neuroscience conference in Chicago, she told delegates there are two central problems. The first is the assumption that stress from major life events can cause depression and the second is that depression is due to an imbalance of neurotransmitters such as serotonin and dopamine.

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Redi studied rats with behavioral and physiological abnormalities found in humans with major depression. First, she isolated the specific genes related to depression in the hippocampus and amygdala regions of the brain. Rats were then exposed to two weeks of chronic stress, so enabling her to identify the genes that responded to stress as well as those that responded to depression. After examining 30,000 genes, she found 254 were related to stress, 1,275 to depression and just five were found in both samples.

From this, Redi concludes that stress does not cause the same molecular changes as depression. The results also suggest that neurotransmitter imbalance may not be the trigger for depression. The real cause of depression, Redi suggests, appears to start in the development and function of neurons. Antidepressant medications act like a band-aid in that they do not target the cause of depression, only the effect. "If depression was related to neurotransmitter activity, we would have seen that," she said.

Sceptics may argue that the function of the rat brain is vastly different to that of a human brain. To this Redi states, "the similarities between these regions of the human and rodent brain are remarkable. The hippocampus and amygdala are part of the so-called ancient lizard brain that controls survival and are the same in even primitive organisms."

Redi states there hasn't been an antidepressant based on new ideas for the past 20 years. She hopes these new findings will promote research into new ways of treating depression.